Heat-sealable polyolefins and articles made therefrom

ABSTRACT

Polyolefins, preferably polyethylene, having a density of about 0.86 to about 0.93 g/mL, and having methyl branches and at least branches of two other different lengths of six carbon atoms or less, form heat seals at exceptionally low temperatures, thereby allowing good seals to be formed rapidly. This is advantageous when heat sealing these polyolefins, for example in the form of single or multilayer films.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119 from U.S.Provisional Application Ser. No. 60/152,701 (filed Sep. 7, 1999), U.S.National Application Ser. No. 09/655,106 (filed Sep. 6, 2000) now U.S.Pat. No. 6,620,897, and U.S. Divisional Application Ser. No. 10/623,045(filed Jul. 18, 2003) now U.S. Pat. No. 6,765,075 which are incorporatedby reference herein as if fully set forth.

FIELD OF THE INVENTION

Polyolefins, preferably polyethylene, having a density of about 0.86 toabout 0.93 g/mL, and having methyl branches and at least 2 otherdifferent lengths of branches of 6 carbon atoms and less, form heatseals at exceptionally low temperatures, thereby allowing good seals tobe formed rapidly. This is advantageous when heat sealing so-calledflexible packaging made from single or multilayer films.

TECHNICAL BACKGROUND

Polyolefins such as polyethylene and polypropylene have been used inmany applications, for example in packaging such as bags and cartons. Inmany instances in order to form the package, it is necessary to effect aseal between two different pieces or two different parts made of thesame polyolefin. This may be done using adhesives, but is more commonlydone by applying heat to the surfaces to be joined to soften or meltthem while applying some pressure to the place where they are to bejoined to form a single piece of thermoplastic. This operation is calledheat sealing, and is commonly used to join thermoplastic parts. See forinstance K. R. Osborn, et al., Plastic Films, Technomic Publishing Co.,Inc., Lancaster, Pa., U.S.A., 1992, especially p. 152–153 and 173–175;H. Mark, et al., Ed., Encyclopedia of Polymer Science and Engineering,Vol. 1, McGraw Hill Book Co., New York, 1985, p. 527; and ibid., Vol. 7,1987, p. 117.

Most commonly, the heating is carried out by contacting the surfacesopposite those to be joined with a hot object such as a hot bar, orheating the surfaces with hot air or infrared radiation. In any event,the speed at which one can heat the surfaces to be joined to the propertemperature for joining often determines the speed at which one canheat-seal the surfaces. This is particularly true for thermoplasticssuch as polyolefins, because they often have relatively low thermalconductivities. High-speed heat sealing is important because many suchoperations are high volume continuous operations where slow heat sealingspeeds significantly increase costs.

One way to increase heat sealing speeds is to lower the temperature atwhich the seal may be formed. This is typically done by lowering themelting point of the polymer being sealed, but has its limits since ifthe melting point of the polymer is lowered too much the seal itself maybe too weak or the polymer characteristics may be detrimentallyaffected. Therefore, ways of forming satisfactory seals at lowertemperatures are constantly being sought.

Numerous attempts have been made to find polymers with improved heatsealing properties, see for instance U.S. Pat. No. 5,358,792, U.S. Pat.No. 5,372,882, U.S. Pat. No. 5,427,807, U.S. Pat. No. 5,462,807, U.S.Pat. No. 5,530,065, U.S. Pat. No. 5,587,247, U.S. Pat. No. 5,741,861,U.S. Pat. No. 5,770,318, U.S. Pat. No. 5,773,106, U.S. Pat. No.5,773,129, U.S. Pat. No. 5,792,549, WO9303093, WO9532235 and WO9728960.None of these references uses the polymers described herein.

WO9827124, WO9847934, WO9905189, U.S. Pat. No. 5,714,556 and U.S. Pat.No. 5,866,663 and U.S. Pat. No. 6,060,569 (all of which are incorporatedby reference herein for all purposes as if fully set forth) describegenerally certain branched polyolefins, and their uses. The specificpolymers used herein are not particularly noted in these publicationsfor use in heat sealing applications.

SUMMARY OF THE INVENTION

This invention concerns a process for lowering the heat sealingtemperature of a polyolefin-based thermoplastic, comprising the step ofreplacing at least a portion of the polyolefin in the thermoplastic witha branched polyolefin having a density of about 0.86 to about 0.93 g/mL,and having methyl branches and at least branches of two other differentlengths of six carbon atoms or less, provided that said methyl branchesare at least 10 mole percent of total branching in said branchedpolyolefin.

This invention further concerns a first article having a firstthermoplastic surface suitable for heat sealing to a secondthermoplastic surface of the same or another article, wherein said firstthermoplastic surface comprises a branched polyolefin having a densityof about 0.86 to about 0.93 g/mL, having methyl branches and at leastbranches of two other different lengths of six carbon atoms or less,provided that said methyl branches are at least 10 mole percent of totalbranching in said branched polyolefin.

The invention still further concerns a process for preparing an articlecomprising the step of heat sealing a first thermoplastic surface to asecond thermoplastic surface, wherein the first thermoplastic surfaceand the second thermoplastic surface comprise a branched polyolefinhaving a density of about 0.86 to about 0.93 g/mL, having methylbranches and at least branches of two other different lengths of sixcarbon atoms or less, provided that said methyl branches are at least 10mole percent of total branching in said branched polyolefin.

This invention also concerns an article made at least in part from afirst thermoplastic surface and a second thermoplastic surface joinedtogether by heat sealing, wherein the first thermoplastic surface and asecond thermoplastic surface comprise a branched polyolefin having adensity of about 0.86 to about 0.93 g/mL, having methyl branches and atleast branches of two other different lengths of six carbon atoms orless, provided that said methyl branches are at least 10 mole percent oftotal branching in said polyolefin.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The polymers used herein are hydrocarbon polyolefins, that is polymersmade by the addition polymerization of olefinic bonds of one or morehydrocarbon olefins. Preferably the polymers are made from one or moremonomers (olefins) of the formula R¹HC═CHR², wherein R¹ and R² are eachindependently hydrogen or alkyl; more preferably wherein one of R¹ or R²is hydrogen, and the other is hydrogen or n-alkyl, and especiallywherein both R¹ and R² are hydrogen (the olefin is ethylene). A specificpreferred polymer is polyethylene, that is a polymer containing about 80mole percent or more of repeat units derived from ethylene, and anotherspecifically preferred polymer is homopolyethylene, which contains about98 mole percent or more of repeat units derived from ethylene.

The polymers useful herein are obtainable (and preferably obtained) bypolymerizing olefins in the presence of a catalyst component comprisinga late transition metal catalyst such as, for example, disclosed inpreviously incorporated WO9827124, WO9847934, WO9905189, U.S. Pat. No.5,714,556, U.S. Pat. No. 5,866,663 and U.S. Pat. No. 6,060,569, as wellas U.S. Pat. No. 5,852,145, U.S. Pat. No. 5,880,241, U.S. Pat. No.5,932,670, U.S. Pat. No. 5,942,461, WO98/30612, WO98/37110, WO98/40374,WO98/40420, WO98/42664, WO98/42665, WO98/47933, WO98/47934, WO99/30609,WO99/49969, WO99/41290 and WO99/62968 (all of which are alsoincorporated by reference herein for all purposes as if fully setforth). Preferably, the polymers are made by polymerizing an olefincomponent comprising a predominant amount of ethylene, in the presenceof a catalyst component comprising a late transition metal complex (morepreferably wherein the late transition metal is Ni or Pd) of a diimineligand. One such preferred late transition metal complex is set forth inthe examples appended hereto. The catalyst component may also optionallycontain various suitable catalyst activators and co-catalysts. Furtherdetails regarding the catalyst component may be had by reference to thepreviously incorporated publications.

Although any type of polymerization process, gas phase, slurry, orsolution, continuous, batch or semibatch, may be used to prepare thebranched polyolefins suitable for use herein, because of the relativelylow melting point of these polyolefins, it is preferred to make them ina solution or slurry process, more preferably a solution process.

The branched polyolefins have a density of about 0.86 to about 0.93g/mL, preferably about 0.86 to about 0.91 g/mL, and especially about0.88 to about 0.90 g/mL, at 23° C. The density, as is usually done, ismeasured on solid polymer without filler or other materials (except fornormal small amounts of antioxidants) using the method of ASTM D1505.

Consistent with the requirements for density and as otherwise set forthabove, the polyolefins utilized in accordance with the present inventioncontain at least some branching. Measurement (usually by ¹³C NMR) andcalculation of branching levels in these polymers is described in thepreviously incorporated publications, and reference may be had theretofor further details.

These polymers have branches of at least three different lengthscontaining 6 carbon atoms or less, or in other words at least any threeof methyl, ethyl, n-propyl, n-butyl, n-amyl and n-hexyl. Usually n-hexylis lumped together as hexyl+, meaning n-hexyl plus any other longerbranches. For the purposes herein n-hexyl means hexyl+ also (forbranches longer than ethyl the “n−” may be omitted), and all hexyl+branches are considered to contain 6 carbon atoms. It is preferred thatat least four different branch lengths containing six or fewer carbonatoms be present.

Some of the polymers suitable for use in accordance with the presentinvention, and prepared in accordance with the previously incorporatedreferences, have unusual branching, i.e., they have more or fewerbranches than would be expected for “normal” coordinationpolymerizations, or the distribution of sizes of the branches isdifferent from that expected, and “branches on branches” may alsopresent. By this is meant that a branch from the main chain on thepolymer may itself contain one or more branches. It is also noted thatthe concept of a “main chain” may be a somewhat semantic argument ifthere are sufficient branches on branches in any particular polymer.Thus, a “branch” hereunder refers to a methyl group connected to amethine or quaternary carbon atom, or a group of consecutive methylenesterminated at one end by a methyl group and connected at the other endto a methine or quaternary carbon atom. The length of the branch isdefined as the number of carbons from and including the methyl group tothe nearest methine or quaternary carbon atom, but not including themethine or quaternary carbon atom. If the number of consecutivemethylene groups is “n” then the branch contains (or the branch lengthis) n+1. Thus the structure (which represents part of a polymer)—CH₂CH₂CH[CH₂CH₂CH₂CH₂CH(CH₃)CH₂CH₃]CH₂CH₂CH₂CH₂— contains 2 branches, amethyl and an ethyl branch.

At least about 10 mole percent of the branches in the polymer,preferably at least about 25 mole percent, more preferably at leastabout 60 mole percent, are methyl branches. By this is meant that thetotal length of the branch (as defined above) from the nearest branchpoint is one carbon atom. In this calculation, ends of chains areexcluded (corrected for), using the number average molecular weightdetermined by Gel Permeation Chromatography, using a suitable standard(calibration by light scattering is preferred). It is also preferredthat the polymer have (in combination with the above) one or more of: atleast about 10 mole percent, more preferably at least about 15 molepercent of the branches are ethyl; at least about 3 mole percent, morepreferably at least about 5 mole percent of the branches are propyl; atleast about 3 mole percent, more preferably at least about 5 molepercent of the branches are butyl; at least about 2 mole percent, morepreferably at least about 4 mole percent of the branches are amyl;and/or at least about 3 mole percent, more preferably at least about 5mole percent of the branches are hexyl+.

In one preferred embodiment, the polymer contains about 30 to about 150branches per 1000 methylene groups, and which contains for every 100branches that are methyl, about 30 to about 90 ethyl branches, about 4to about 20 propyl branches, about 15 to about 50 butyl branches, about3 to about 15 amyl branches, and about 30 to about 140 hexyl+ branches.

In another preferred embodiment, the polymer contains about 20 to about150 branches per 1000 methylene groups, and which contains for every 100branches that are methyl, about 4 to about 20 ethyl branches, about 1 toabout 12 propyl branches, about 1 to about 12 butyl branches, about 1 toabout 10 amyl branches, and 0 to about 20 hexyl+ branches.

It is further preferred that the branched polyolefins are polyethylenes,more preferably homopolyethylenes.

Another preferred embodiment is a homopolyethylene containing thestructure (XXVII) in an amount greater than can be accounted for by endgroups.

More preferably this homopolyethylene contains about 2 or more of(XXVII) per 1000 methylene groups.

In accordance with one aspect of the present invention, the heat sealingtemperature of a polyolefin-based thermoplastic can be lowered byreplacing at least a portion of the polyolefin in the thermoplastic withthe branched polyolefin as described above. The branched polyolefin cansimply be used in place of the original polyolefin, or can be blended invarious proportions with the original polyolefin in order to replace aportion of the same. Such a blend can be a standard physical blend, meltblend, or even a reactor blend prepared by polymerizing the desiredolefins in the presence of the catalyst composition referred to above,along with a second active polymerization catalyst (a co-catalyst) suchas a Ziegler-Natta and/or metallocene-type catalyst known in the art,used to prepare the original polyolefin. See, for example, U.S. Pat. No.6,114,483, WO97/48735, WO97/38024 and WO98/38228 (all of which are alsoincorporated by reference herein for all purposes as if fully setforth).

The resulting thermoplastic can be used to form articles with surfacespossessing a lower heat sealing temperature and, thus, improvedprocessibility.

In preparing articles by heat sealing thermoplastic surfaces, it ispreferred that all of the respective surfaces comprise the branchedpolyolefin as described herein. More preferably, the various surfacesare made essentially only with the branched polyolefins described aboveas the thermoplastic polymer, still more preferably from such branchedpolyolefins prepared from the same monomer(s), and especially when eachof the surfaces is the same polymer. Of course, in addition to thebranched polyolefins (and other thermoplastic polymer components), thesurfaces can contain other additives and adjuvants commonly found inheat sealing thermoplastics such as, for example, antioxidants andstabilizers, colorants, processing aids and the like.

More than two surfaces may be sealed together, for example three filmsmay be sealed together, and preferably all of the surfaces being sealedare of the same branched polymer as described herein.

Heat sealing may be done by any variety of methods well known to thoseskilled in the art. See for instance Plastic Films, Technomic PublishingCo., Inc., Lancaster, Pa., U.S.A., 1992, especially p. 152–153 and173–175. Preferably the heating of the areas to be sealed is done bythermal conduction from a hotter material (e.g., sealing bar(s) orroller(s)), by microwave heating, dielectric heating, and ultrasonicheating. The amount of pressure used may vary from that needed tocontact the two (or more) surfaces to be sealed, for example fingerpressure to pressure applied by presses or rollers, for example up to700 kPa (100 psi). The heating may be before, or simultaneous with theapplication of pressure. Although pressure may be applied beforeheating, it will normally not be effective until the heating is carriedout. Generally speaking, the temperatures of the polyolefin surface thatis being sealed will be about 50° C. to about 110° C. This temperaturewill depend to some extent on the amount of pressure used, higherpressures allowing lower temperatures, since higher pressures cause moreintimate contact between sealing surfaces. It also depends on thepolyolefin of the heat-sealing surface, and those with lower densitieswill usually have lower sealing temperatures. Since much of the heatsealing done commercially is on high speed lines, the lower thetemperature needed to give a seal of sufficient strength, the faster theline may often run, since it will take less time to heat the sealingsurfaces to the required temperature.

The materials which may be heat-sealed are any whose surface to beheat-sealed is of the polyolefins used herein. Useful materials whichmay be heat sealed include single and multilayer films, polyolefincoated paper or paperboard, polyolefin coated metal foil (which can beconsidered a multilayer film), polyolefin coated articles made byinjection or blow molding, polyolefin injection or blow molded articles,rotationally molded parts. Preferred materials for heat sealing aresingle and multilayer blown and/or oriented films and sheet, coatedpaper and paperboard, and single and multilayer films are especiallypreferred. A single layer film will simply be a layer of the polyolefinsdescribed herein. A multilayer film will have two or more layers, andone or both of the surface layers will be a polyolefin described herein.For example other layers may be present for the purposes of increasedbarrier properties to one or more materials, for added strength and/ortoughness, for decorative purposes (for example to have been or beprinted on), adhesive layers to improve adhesion between other layers,or any combination of these. These other layers may be polymers such aspolyolefins, polyesters, polyamides, polycarbonates, acrylics, ormixtures of these, paper, and metal (foil).

The present process is particularly useful to form packages, which arealso particularly useful articles. By a “package” is meant any containerthat is meant to be sealed most of the time (sometimes called“protective packaging”), especially before the contents are used,against ambient conditions such as air and/or moisture, and/or loss ofthe package's content as by evaporation. The package may be designed sothat the seal against ambient conditions may be broken permanentlybroken as by cutting or tearing to open a sealed bag. The package mayhave one or more inlets and/or outlets to store a material that may beadded to and/or withdrawn from the package without further opening thepackage. These packages are preferably made from single or multilayerfilms, especially multilayer films, in which the present polyolefins areat least the “sealing layer” that is the layer that forms a heat seal.These include flexible bags which are sealed, such as solid or liquidfood containers, intravenous bags, pouches, and dry food containers(cereal and cracker liners in boxes).

In the Examples, the following tests were used:

Tensile properties, ASTM D882, Method A (MD is machine direction, TD istransverse direction).

Film density by ASTM D1505.

I₂ and I₁₀ by ASTM D1238.

Elmendorf Tear by ASTM D1922

Heat seals were formed by ASTM F88, using a 12.5 μm (0.5 mil) Mylar®film slip sheet, 138 kPa (20 psi) sealing pressure, a 0.64 cm (0.25″)wide sealing bar, and a 0.25 sec dwell. The heat seal strengths weremeasured on an SP-102C-3m90 Slip/Peel tester supplied by IMASS, Inc.,Box 134, Accord, Mass., 02018, U.S.A., at a 25.4 cm/min (10″/min)crosshead speed.

The commercial polyolefins, all believed made with metallocene-typecatalysts, used in the Comparative Examples were obtained as follows:

Exact® 3128, and Exact® 4033 are reportedly ethylene/1-butene copolymersobtained from Exxon Chemical Corp., Houston, Tex. 77252 U.S.A.

Exact® 3132 and Exact® SLP 9095 are reported to be ethylene/1-hexenecopolymers, obtained from Exxon Chemical Corp.

Affinity® PL 1880 is reported to be an ethylene/1-octene copolymer,obtained from Dow Chemical Co., Inc., Midland, Mich. U.S.A.

EXAMPLES 1–2

General Polymerization Procedure

The solution polymerization system used for this work was a semi-batchtank reactor, and consisted of an 8-L (16.4 cm I.D.×36.7 cm high)vertical stirred stainless steel reactor, gas purification systems,solvent purification systems, an online mass flow rate detector tomeasure ethylene feed rate, and an online GC measurement system toanalyze the head space composition in the reactor. The reactor wasequipped with an agitator, an internal coil and a jacket in whichcirculated a mixture of steam and water. The reactor could be operatedin a temperature range of 20 to 115° C. by adjusting steam and waterflows in the internal coil and jacket. Process temperature, pressure,and mass flow rate of ethylene were measured and recorded online.Research grade ethylene monomer was further purified by passingspecially designed moisture and oxygen traps to remove residualimpurities. Ultra high purity nitrogen/argon were further purified bypassing through their own series of two gas dryers, one carbon dioxideabsorber, and one oxygen trap. High purity solvent was further dried bypassing three specially designed purification columns before added intothe reactor.

The following materials were used for the solution ethylenepolymerizations:

Ethylene monomer (research grade, 99.999 mol. %, Matheson Gas ProductsCanada, Inc., Whitby, ON Canada);

Nitrogen (ultra high purity, 99.999 mol %, Praxair Canada, Inc.,Belleville, ON Canada);

Argon (ultra high purity, 99.999 mol %, Praxair Canada, Inc.);

Toluene (99.9 wt %, anhydrous, Sigma-Aldrich Canada Ltd., Mississauga,ON Canada);

Modified Methylaluminoxane (MMAO-3A) (6.99 wt % of Al in toluene, AkzoNobel Chemical Inc., Chicago, Ill. U.S.A.);

Cyclohexane (Pure grade, 99.94 wt %, Phillips Chemical Company,Bartlesville, Okla. U.S.A.).

The nickel compound used in the catalyst system had the formula as shownbelow:

The following preparation steps were taken prior to polymerization:

-   -   Toluene was distilled in the presence of metallic sodium and        benzophenone.    -   Catalyst was dissolved in the dried toluene.    -   Reactor body was dried at 115° C. for over one hour under vacuum        then purged using dried argon.

Unless otherwise noted, all pressures are gauge pressures.

Typically, an amount of pre-dried solvent (5.0 l) was added into thereactor under a reactor sealed condition. The reactor was heated up to adesired polymerization temperature. Modified methylaluminoxane (Al/Ni of500–900) as a scavenger was injected into the reactor and the contentsin the reactor were mixed with an agitation speed of 400 rpm for 15 min.Ethylene was injected into the reactor to pre-saturate the solvent at apressure of 1.0 MPa.

Nickel compound (2–20 mg) with 50 ml of solvent (toluene) was mixed withmodified methylaluminoxane (Al/Ni: 500–1000) for 5 min and was injectedinto the reactor using ethylene. An additional 100-ml of cyclohexane wasused to wash any catalyst residuals in the catalyst charging port. Thereactor pressure was adjusted to a desired pressure level by regulatingethylene flow rate. Ethylene was continuously charged into the reactorunder agitation. Ethylene mass feed rate was recorded online.Temperature and pressure were maintained at a constant level for a givenpolymerization time (1 to 3 h).

At the end of polymerization, the residual ethylene in the reactor wasvented off after ethylene supply had been shut off. The reactor pressurewas reduced to 0 Pa. The residual catalyst was deactivated by adding asmall amount of methanol into the polymer solution.

The polyethylene was separated from the solution by evaporating thesolvent under a nitrogen purge. The resulting polymer was dried at 60°C. in a vacuum oven over 24 h to remove any residual solvent.

The polymerization conditions for the examples in Table 1 are asfollows:

Cyclohexane: 5.0 l Nickel compound: 20.0 mg Al/Ni ratio: 1000 Reactorpressure: 1.38 MPa Temperature: 65° C.

For the polymer of Example 1, 8 separate polymerizations were run, andthe products combined into a single polymer batch. Polymerization timeswere 1–3 h, and ethylene pressure was 1.0 MPa.

For the polymer of Example 2, 4 separate polymerization runs were made,similar to those for Example 1, except for 3 of those runs the solventwas isooctane and for the fourth cyclohexane, the temperature was 60–65°C., and the ethylene pressure was 1.4–1.7 MPa. The products of all 4polymerization runs were combined into a single batch of polymer.

For Example 1, the polymer from each of the 8 polymerization runs wascut into strips and extruded through a 1.9 cm (0.75″) Killion singlescrew extruder and cut into pellets. The pellets from all 8polymerization runs were then blended together and mixed with 500 ppm ofIrgafos® 168 and 500 ppm of Irganox® 1076 antioxidants (Ciba-GeigyCorp.), and the entire batch extruded through the same extruder andformed into pellets. For all of these extrusions, the rear zone was 180°C., all the other zones 190° C., and screw rpm was 60 for the individualbatches and 75 for the combined batch.

For Example 2, the polymer from each of the 4 polymerization runs wascut into strips and extruded through a 1.9 cm (0.75″) Killion singlescrew extruder and cut into pellets. The pellets from all 4polymerization runs were then blended together and mixed with 500 ppm ofIrgafos® 168 and 500 ppm of Irganox® 1076 antioxidants (Ciba-GeigyCorp.), and the entire batch extruded through the same extruder andformed into pellets. For individual batch extrusions, the rear zone was170° C., all the other zones 180° C., and screw rpm was 61.5, and forthe single combined batch the rear zone was 180° C., all the other zones190° C., and the screw rpm was 50.

EXAMPLE 3 AND COMPARATIVE EXAMPLES A–D

The polyethylene of Example 1 and three commercial copolymers ofethylene and an alpha-olefin were extruded through a blown film die, andwound up. The extruder was a 1.7 cm (0.75″) diameter Killion 30/1 L/Dsingle screw extruder fitted with a 2.5 cm (1″) diameter Killion blownfilm die and a Future Design Saturn® mini air ring. The rear zone was180° C., the other barrel zones 200° C., the adapter 220° C., and thedie zones 190–200° C., and the screw rpm 60. The film gage was nominally50 μm (2 mil), the layflat dimension was 12.1 cm (4.75″), and blow-upratio 3:1. Frostline heights are given in Table 1. Table 1 also listsheat seal strengths and densities for the various polymers.

TABLE 1 Example 3 A B C Polymer Ex. 1 Exact ® 3132 Exact ® 4033 Exact ®SLP9095 Frost Line (cm) 12.1 15.9 14.0 12.7 Film Density, 0.889 0.9030.885 0.886 g/ml Thickness, μm 50.5 53.3 55.9 53.3 Heat Seal Strengths,gm/1.27 cm  60° C. 0  65° C. 121 0  70° C. 302 11  75° C. 325 0 227  80°C. 290 203 313  85° C. 317 265 307  90° C. 336 0 241 348  95° C. 273 450235 284 100° C. 303 504 245 339 105° C. 307 464 252 320 110° C. 299 439252 363

EXAMPLE 4 AND COMPARATIVE EXAMPLES D–G

The polyethylene of Example 2 and four commercial copolymers of ethyleneand an alpha-olefin were extruded through a blown film die, and woundup. Extrusion conditions were the same as in Example 3, except thelayflat was 13.3 cm for Example 4 and 12.7 cm for Comparative ExamplesD–G. Frostline, density, thickness and heat seal strengths are given inTable 2, and other physical properties are given in Table 3.

TABLE 2 Example 4 D E F G Polymer Ex. 2 Exact ® Exact ® Affinity ®Exact ® 3128 3132 PL1880 4033 Frost Line (cm) 16.5 12.7 15.2 13.3 15.9Film 0.895 0.903 0.903 0.905 0.886 Density, g/ml Heat Seal Strengths,gm/1.27 cm  70° C. 0  75° C. 60 0  80° C. 296 180  85° C. 354 276  90°C. 368 292  95° C. 391 10 0 0 295 100° C. 350 242 98 52 332 105° C. 341525 443 365 310 110° C. 360 533 568 523 311 115° C. 358 485 590 571 274120° C. 365 531 590 541 273

TABLE 3 Example 4 D E F G Polymer Ex. 2 Exact ® Exact ® Affinity ®Exact ® 3128 3132 PL1880 4033 I₂ 0.940 1.140 1.180 1.030 0.800 I₁₀ 6.2106.600 6.920 8.770 4.450 I₁₀/I₂ 6.6 5.8 5.9 8.5 5.6 Tensile Properties MDTensile 42.0 43.1 47.3 43.8 49.2 Strength MPa Elong. 817 892 856 840 834Break,% 1% Secant 21.6 52.9 57.7 64.4 16.7 Mod., MPa TD Tensile 43.338.4 48.5 37.0 41.4 Strength Mpa Elong. 795 861 865 807 720 Break, % 1%Secant 20.6 50.3 59.2 61.9 15.7 Mod., MPa Elmendorf, g/25 μm MD 93.8144.6 193.4 262.7 40.9 TD 107.6 171.0 233.1 263.9 25.1

Table 4 lists the branching levels of various polymers used in theExamples, as determined by ¹³C NMR. In Table 4, EOC is ends-of-chains.Total methyl indicates the total number of branches plus EOC, whilemethyl indicates the amount of actual methyl branches, both as definedherein.

TABLE 4 Branching per 1000 CH₂'s Hex+ Total and Polymer Methyl MethylEthyl Propyl Butyl Amyl EOC Example 2 59.4 37.2 6.3 3.4 2.9 1.7 5.8Example 1 60.8 41.0 5.6 2.7 2.8 1.8 6.4 Exact ® 54.0 0.0 54.0 0.0 0.00.0 0.0 4033 (film) Exact ® 43.1 0.0 2.5 0.0 39.2 0.0 0.8 SLP 9095(film)

Table 5 lists the results of hot tack tests on various polymers. Thetest used was the “Packforsk” test, using a pressure of 280 kPa (40 psi)and a dwell time of 3 sec. This test is described in A. M. Soutar,Journal of Plastic Film and Sheeting, Vol. 12, p. 304–334.

TABLE 5 Polymer Ex. 1 Ex. 2 Exact ® 4033 Temp., ° C. Strength, N/cm  801.6 3.0 4.7  90 5.2 2.6 3.9 100 5.4 2.5 3.3 120 4.1 3.0 3.9 140 5.1 3.05.0 160 4.8 3.0 4.0 180 5.1 2.9 4.5 200 4.0 2.3 4.3 220 4.1 2.0 3.3

1. A process for lowering the heat sealing temperature of apolyolefin-based thermoplastic, comprising the step of replacing atleast a portion of the polyolefin in the thermoplastic with a branchedpolyolefin having a density of about 0.86 to about 0.93 g/mL, and havingat least three of methyl, ethyl, n-propyl, n-butyl, n-amyl and n-hexylbranches.
 2. The process as recited in claim 1, wherein the branchedolefin is obtainable by polymerizing an olefin in the presence of acatalyst component comprising a late transition metal catalyst.
 3. Theprocess as recited in claim 2, wherein the late transition metalcatalyst is a late transition metal complex of a diimine ligand.
 4. Theprocess as recited in claim 1, wherein the branched polyolefin has adensity of about 0.86 to about 0.91 g/mL.
 5. The process as recited inclaim 1, wherein said branched polyolefin is a homopolyethylene.
 6. Afirst article having a first thermoplastic surface suitable for heatsealing to a second thermoplastic surface of the same or anotherarticle, wherein said first thermoplastic surface comprises a branchedpolyolefin having a density of about 0.86 to about 0.93 g/mL, and havingat least three of methyl, ethyl, n-propyl, n-butyl, n-amyl and n-hexylbranches.
 7. The first article as recited in claim 6, wherein thebranched olefin is obtainable by polymerizing an olefin in the presenceof a catalyst component comprising a late transition metal catalyst. 8.The first article as recited in claim 6, wherein the first article is aflim.
 9. The first article as recited in claim 6, wherein the branchedpolyolefin has a density of about 0.86 to about 0.91 g/mL.
 10. The firstarticle as recited in claim 6, wherein said branched polyolefin is ahomopolyethylene.
 11. A process for preparing an article comprising thestep of heat sealing a first thermoplastic surface to a secondthermoplastic surface wherein the first thermoplastic surface and thesecond thermoplastic surface comprise a branched polyolefin having adensity of about 0.86 to about 0.93 g/mL, and having at least three ofmethyl, ethyl, n-propyl, n-butyl, n-amyl and n-hexyl branches.
 12. Theprocess as recited in claim 11, wherein the branched olefin isobtainable by polymerizing an olefin in the presence of a catalystcomponent comprising a late transition metal catalyst.
 13. The processas recited in claim 11, wherein the article is a single or multilayerfilm.
 14. The process as recited in claim 11, wherein said branchedpolyolefin has a density of about 0.86 to about 0.91 g/mL.
 15. Theprocess as recited in claim 11, wherein said branched polyolefin is ahomopolyethylene.
 16. An article made at least in part from a firstthermoplastic surface and a second thermoplastic surface joined togetherby heat sealing, wherein the first thermoplastic surface and a secondthermoplastic surface comprise a branched polyolefin having a density ofabout 0.86 to about 0.93 g/mL, and having at least three of methyl,ethyl, n-propyl, n-butyl, n-amyl and n-hexyl branches.
 17. The articleas recited in claim 16, wherein the branched olefin is obtainable bypolymerizing an olefin in the presence of a catalyst componentcomprising a late transition metal catalyst.
 18. The article as recitedin claim 16, wherein the article is a single or multilayer film.
 19. Thearticle as recited in claim 16, wherein the branched polyolefin has adensity of about 0.86 to about 0.91 g/mL.
 20. The article as recited inclaim 16, wherein said branched polyolefin is a homopolyethylene.